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Rover's Batteries Charged Successfully, But Communication
Spotty

The team operating NASA's Mars
Exploration Rover Spirit is examining data received from Spirit in
recent days to diagnose why the rover apparently rebooted its
computer at least twice over the April 11-12 weekend.

"While we don't have an explanation yet, we do know that
Spirit's batteries are charged, the solar arrays are producing
energy and temperatures are well within allowable ranges. We have
time to respond carefully and investigate this thoroughly," said
John Callas of NASA's Jet Propulsion Laboratory, Pasadena, CA,
project manager for Spirit and twin-rover Opportunity. "The rover
is in a stable operations state called automode and taking care of
itself. It could stay in this stable mode for some time if
necessary while we diagnose the problem."

Spirit communicated with controllers Friday, Saturday and
Sunday, but some of the communication sessions were irregular. One
of the computer resets apparently coincided in timing with
operation of the rover's high-gain dish antenna.

The rover team has the advantage of multiple communication
options. Spirit can communicate directly with Earth via either the
pointable high-gain antenna or, at a slower data rate, through a
low-gain antenna that does not move. Additionally, communications
can be relayed by Mars orbiters, using the UHF (ultra-high
frequency) transceiver, a separate radio system on the rover.

"To avoid potential problems using the pointable antenna, we
might consider for the time being just communicating by UHF relay
or using the low-gain antenna," Callas said.

Spirit finished its three-month prime mission on Mars five years
ago and has kept operating through multiple mission extensions.

The rover's onboard software has been updated several times to
add new capabilities for the mission, most recently last month. The
team is investigating whether the unexpected behavior in recent
days could be related to the new software, though the same software
is operating on Opportunity without incident.

"We are aware of the reality that we have an aging rover, and
there may be age-related effects here," Callas said.

In the past five weeks, Spirit has made 119 meters (390 feet) of
progress going counterclockwise around a low plateau called "Home
Plate" to get from the place where it spent the past Martian winter
on the northern edge of Home Plate toward destinations of
scientific interest south of the plateau. On March 10, after
several attempts to get past obstacles at the northeastern corner
of Home Plate, the rover team decided to switch from a clockwise
route to the counterclockwise one. Subsequent events have included
Spirit's longest one-day drive since the rover lost use of one of
its wheels three years ago, plus detailed inspection of light-toned
soil exposed by the dragging of the inoperable wheel.

Halfway around Mars, meanwhile, Opportunity has continued
progress on a long-term trek toward Endeavour Crater, a bowl 22
kilometers (14 miles) in diameter and still about 12 kilometers (12
miles) away. Last week, a beneficial wind removed some dust from
Opportunity's solar array, resulting in an increase by about 40
percent in the amount of electrical output from the rover's solar
panels.